Color television sampling system



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June 30, 1953 R, Q MOORE COLOR TELEVISION SMPLING SYSTEM s sheets-sheet2 Filed March 16, 1951 IN VEN TOR ORT C. D700/Q6 ullugv.'

June 30, 1953 R. c. MOORE COLOR TELEVISIONVSAMPLING SYSTEM.

Fil`ed March 16, 1951 3 Sheetji--Sheec'l 3 Y INVENToR.

Rosan c. mao/u Patented June 30, 1953 aan,

COLOR TELEVISION SAlYlPLING SYSTEM Robert C. Moore, Erdenheim, Pa.,assignor to Philco Corporation, Philadelphia, Pa., a corporation ofPennsylvania Application March 16, 1951, Serial No. 215,996

18 Claims.

The present invention relates to electrical systems and moreparticularly to electrical systems for transmitting a plurality ofintelligence components over a single channel. The invention isparticularly applicable toand will be described in connection with acolor television system in which signals, each representative of oneofthe primary color components of the individual picture elements of theimage televised, are transmitted over a single carrier medium inso-called dot-sequential arrangement.

`In the so-called dot-sequential system for transmitting a colortelevision image, the image toV be transmitted is analyzed dot-by-dot bymeans of a sampling technique producing a series of pulses of videosignal energy with the amplitude of each such pulse being determined bythe ordinate of the video signal at the precise instant at which thepulse is developed. For example, three component color signals may berespectively developed by three separate camera tubes and the signalwhich is produced by each of the camera tubes and which is continuouslypresent, is sampled in some preferred manner so as to yield acomponent-color pulse train. By means 1- of multiplexing, the threecomponent-color pulse trains are interleaved into a composite-colorpulse train.

The composite-pulse train is then filtered by means of a suitable lowpass filter and thereafter transmitted in any suitable manner. Becauseof the frequency band limitation imposed by the low pass filter, thevideo wave produced at the transmitter in the above described system iseffectively a composite sine wave superimposed on a f.

unidirectional reference component. The said sine wave has a frequencyequal to the frequency at which each of the color signals is sampled andthe said reference component and the amplitude and phase position of thesine wave are determined by the magnitudes of the component colorpulses. At the receiver positionthe incoming video signal is supplied toa suitable sampling or equivalent system by means of which there arederived therefrom the individual three color components each bearing thedesired color information.

Since in the transmitted video signal, the color information is sampledat equal time intervals, each color component in effect utilizesone-third Vof the available transmission facilities.

In the foregoing and following discussion it is assumed that the threecomponent signals s ampled at the transmitter correspond to a primarycolor system made up of the green, red

- 2 and 4blue color components of the image to be televised. However,asis well known from the' principles of colorimetry, a given visualsensation may be equally produced by other primary color systems thecomponents of which are suitably selected to produce the required valuesof luminosity and chromaticity. Furthermore, the spectrum distributionof the green signal can be made to approximate the responsecharacteristic of the eye, whereby this signal approaches thecharacteristics of a panchromatic signal and the transmission system mayreadily be modified to utilize such a green signal as a luminosity orbrightness signal indicative ofV image detail with improvement of theresultant image. In such a modified arrangement appropriate red vminusluminosity and blue minus luminosity signals are utilized lforestablishing the chromatic character-'- istics of the image.

It has been found that physiologically, the hu-` man eye is relativelyinsensitive to color in fine areas. Furthermore, in practice it appearsthat the eye is less sensitive in distinguishing detail presented incertain colors than it is in distinguishing detail presented in othercolors. In other words it seems that the eye is less sensitive tochanges in chromaticity than to changes in brightness and thus requiresless information pertaining to chromaticity.

Because of this behavior peculiar to the eye,

an equal utilization of the transmission channel' by each of the threeprimary color component signals is not a most efficient utilizationofthe available transmission channel. More particularly, if it be assumedthat the color television information is to be transmitted over achannel which has a band width of 4 megacycles per second, an equalutilization of this channel by the three primary color component signalswould mean that each component signal contains in-A the eye, this degreeof definition is greater thanA that necessary to satisfy the eye.

It is an object of the invention to provide a ble to color television,in which systems a maxi# mum of information concerning,iinedetails-.fofs an image to be televised is;transmittedfto thereceiving position and only sumcient information conceining thechromaticity of theeimage` isf'` transmitted. Y

Another object of the invention is tov providea transmission receivingsystem fora plurality ofY intelligence signalsin which systemxthere oc-Vcurs a minimum of detectable interference bee tween the respectiveintelligence signals.

These and further objects-of theinvention will. appearsasr thespecification progresses.v

The foregoing objects-arey achieved in accordance with the invention, bymeansof -a system in' which. two signals each vrepresentative of Y givenintelligence are'transmitted simultaneously over a single channel. Bycombining the signals ina given specific manner at the transmitterposition and by separating the signals in a complementary manner at thereceiver position, the original information contained'ineach signal maybe derived without there occurring significant contamination ofonesignal by the other. More particularly, and in one aspect of theinvention, afirst'carrier wave of given frequency and phase is modifiedby a rst intelligence component to` be. transmitted. The' modified firstcarrier is combined with a second carrierv wave-modied by a:second-intelligence component andhavingthesame frequency asthe iirstcarrier wave but having aphase in quadrature with the rst carrier wave.At the receiving position `there is pro.- vided a sampling system or itsequivalent, which samples the rst carrier at its peak voltage pointsandthe second carrier at its Zero voltage points)V thus producing anoutput voltage indicative of the peak values of the first carrierwaveand correspondingly the first intelligence. By means of asecond samplingsysem operating inphase quadrature-to vthe iirst andwhichisamples `thesecond carrier at its peak voltage values. and the. first carrierat itszero voltage values, a secondzoutput: voltage isfproducedindicative of.the peak-valuesofthesecond carrier wave and hence indicativeY ofthesecond intelligence.

In anotheraspect of the invention; as particularlyappl-ied .toa-color-televisicn system in .which theimage elements are reproduced bythree com-- ponentv signals which may each be indicative of a primarycolor component of the color of the image elements or which may beindicative of the luminosity and chromatic aspects ofthe-image elements,there is. provided a suitable sampling or; equivalent systemby means. ofwhich two of the. component signals are added together to produce. a rstcarrier wave ofv given frequency and phase and having a reference leveland am-A plitude. proportional tothe intensities of the so combinedcomponent signals. There is furtherv provided a second sampling orequivalent systemY by means of which the third component signal ismcdiedto produce a secondcarrier kwave of the said given frequency andin phase quadrature to the rst carrier wave and having an amplitudeproportional to the amplitude of the third component signal. The twocarrier waves so produced are combined to produce a resultant wave whichis transmitted over a suitable channel and at the receiving position theoriginal intelligence ccmponents arerestored by meansfof complementarysampling systems.

In a further aspect of the invention as particularly applied to a colortelevision system as above outlined, there is` provided means by whichone of' theA component signals provides a reference wave having;amplitude variations proportional "to: the'zvariationsof'V the saidcomponent signal.

variable reference level and variable amplitude and phase as determinedby the amplitudesof: By meansfof a` complementary sampling-system atthe-.receiver thezoriginal component signals.

position, the original intelligence is recovered.`

so correlated with respect tothe allowable-band width of thetransmission channel .andthe fre-- quency of the carrier. wave as topermit a greater i band width for another component signalcarryv ing-a,greater desired degree of informationwith-.- out exceeding thecapabilities.ofthetransmissionchannel and without introducing signicant.con-- tamination of the Y component signals.:

The invention willbe described in greaterdee tail with reference to theappended. drawings forming partof the specification and in which:

Figure 1 is a schematic diagramof a signalr transmission system inaccordancewith the invention,

Figure 2 is' a schematic` diagram of a system inaccordance -with aVsecondembodiment of the invention particularly applicable for thetrans-Y mission and reception of color television signals, and

Figure/3 is a schematic diagram of a system in accordance with a thirdembodiment ofthe invention'andapplicable for the transmission andreception .of color television signals.

ReferringtoFigure .1, the. system thereshown comprises rst and secondsampling tubes l0 and I2 respectively, whichY operate to sample. insequence signal waves appearing, at input termi.- nals zand 22respectively. Sampling tube l0 may comprise a pentagrid vacuum tubewhich.

has itssuppressorand cathode groundedits second and fourth gridsconnected to a suitable source of .positive screen potential, its .thirdgridV supplied with the signal wave from terminal 20, its first gridsupplied with a sampling signal for rendering the tube conductive onlyduringpredetermined portions of the sampling signal, anditsanodevconnectedto a source of positive potential designatedB-ithrough a load resistorV I4.

Samplingtube. l2 may be. substantially identical with sampling tube Il),being supplied at its third grid with the signal wave from inputterminal 22, and having its anode connected to the source of potentialB+ through the common load. resistor I4. By supplying each ofthesampling,

The threewavesso. produced areV combined and bring abouti an:-outputwave'at the carrier frequency havingfa,

tubes, at the rst grids thereof, with sampling signals derived from anoscillator source I6 and Whose positive peak values occur in 90 phaserelationship, the sampling tubes are made conductive in consecutiveorder. The'design of oscillator source I6 conforms to the usual practiceand the two sampling voltages in phase quadrature may be derivedtherefrom in well known manner, for example by suitable phase shiftingnetworks embodied in the oscillator source.

In order to maintain sampling tubes I0 and I 2 non-conductive exceptduring the period when the sampling signals applied thereto have highpositive peak values, suitable resistance-capacitance networks may becontained in the rst grid circuits of these tubes. More particularly,sampling tube III is provided with a resistancecapacity network I6having a time constant sufciently long compared to the period of thesampling signal from the source I6, so that leveling upon peaks of thesampling signal supplied thereto takes place and conduction through thesampling tubes occurs only during a predeter mined brief intervalsurrounding the time at which the sampling signal attains its peakvalues. A similar network I9 is provided in the first grid circuit ofthe tube I2. I

The output voltage appearing across the load resistor I4 and derivedfrom vthe sampling tube I0 consists basically of a series of pulses eachhaving a duration substantially equal to the length of the conductingperiod of the sampling tube and recurring at the frequency of thesampling signal from the source I6. Successive pulses have amplitudevalues determined by the amplitude of the signal wave applied at theinput terminal 20. These pulses have been shown in the curve adjacent tothe sampling tube II] and are indicated by the numeral 24.

In similar manner, the output voltage derived from the sampling tube I2consists basically of a series of pulses each having a durationsubstantially equal to the length of the conducting period of thesampling tube I2 and recurring at the frequency of the sampling signal.The amplitude values of these pulses are determined by the amplitude ofthe signal wave at the input terminal 22 at the instant of sampling.These pulses have been shown in the curve adjacent to the tube I2 andare indicated by the numeral 26. As will be noted, the pulses 26 occurat a time one-fourth of a cycle later than the pulse 24 in view of thequadrature displacement of the peaks of the sampling signals from thesource I6.

The pulses 24 and 26 are supplied to a filter 28 which eifectivelyconverts each series of pulses into corresponding sine waves having afrequency equal tothe sampling frequency and having a phase quadraturerelationship. These sine waves have been superimposed on the pulses 24and 26 and are shown in Figure 1 as 30 and 32 respectively. Since thetwo sine waves 30 and 32 kare in phase quadrature and are algebraically.occur at the sampling frequency rate.

sition 40 a resultant wave exists similar lto that appearing at theoutput ofthe filter 28 and this wave is applied to the two samplingtubes 42 and 44. Sampling tubes 42 and 44 may be similar to samplingtubes I0 and I2 each being provided with a third grid to which thereceived Wave is applied, a rst grid to which a sampling signal isapplied and an anode which is energized from the B-fsupply throughindividual load resistors 46 and 48 respectively.

Resistance-capacitance networks 50 and 52 are contained in the gridcircuits of the respective tubes 42 and 44 to limit the conductionperiod of the tubes to the intervals during which the peak positivevalues of the sampling signals occur. As a source of sampling signalsforthe tubes 42 and 44 there is provided an oscillator 54 similar to andoperating at the same frequency as the oscillator source I6 andproviding two sampling signals at 90 phase relationship.

The sampling tubes 42 and 44 operate to sample the wave at the position40 in sequence and at time intervals displaced by 90 of the period ofthe sampling signal. Thus sampling tube 42 samples the received wave atthe instant thereof corresponding to the peak amplitude value of theVwave 30, at which time the wave 32 has a zero value. At an interval 90later, the tube 44 samples the received wave and at this time theamplitude value thereof corresponds to the peak value of the wave 32 andzero value of the wave 30.

The voltage appearing across the load resistors 46 `and 43 of therespective sampling tubes is basically constituted by a series of pulseswhich corresp-ond to the pulses 24 and 26 respectively and By means oflow pass filters 56 and 56, these pulses are in tegratedv and signalwaves corresponding t-o the signal. .waves at input terminals 20 and 22are produced at theoutput terminals 60 and 62 respectively.

In the system above described the band width of the lter 28 is theallowable band width of the transmission channel and in an illustrativeexample, the channel may have a band width from 3 to 4 rnc/sec. With adual side band systern operating with the above-noted channel bandwidth, the sampling signal source I6 may have a frequency of 3.5rnc/sec. and the band width of each of the signal waves at the inputs 20and 22 may extend from 0 to 0.5 inc/sec.

By a suitable selection of the frequency of the sampling signal sourcei6, whereby one side band of the output wave is 'partly or whollysuppressed, an amount of intelligence greater than above indicated maybe transmitted over the system of Figure l. More particularly, with atransmission system having an allowable band width of l mc./sec. aspreviously described and as determined b-y the 3-4 rnc/sec. filter 28,and by the use of a sampling source I6 having a frequency of 3.75rnc/sec., input signal waves having a spectrum. extending toapproximately 0.75 rnc/sec. may be transmitted over the system. Underthese conditions the component waves 60 and 32 which make up theresultant wave at the output of the filter 2i! may each be considered asa carrier wave of 3.75 rnc/sec. with an attendant lower side bandspectrum determined by the frequency components of the respective signalwaves at the Y inputs 20 and 22. In such a suppressed side band systemthe carrier waves are in effect each phase modulated to a certain degreeat a rate deter,- mined by the modulation frequency and, because of :thephaseshiftssointroduced, acertain degree of interaction may :occur whenthe ,component waves .30 and 32 are `added together in the filter 28.The degree :of .contamination of one wave by the other :in lsuch aisystem :is largely `determined by the vmaximum Afrequency value of therespective signal waves at the input 'terminals 20 and 22.

In certain instances, for example, as is later more fully discussed inconnection with the ernbodiments of the vinventionshotvn in Figures 2and 8, the :information required at the receiving position'maybesupplied by means of a first signel Shaving a rather large frequencyspectrum vand a vsecond signal having a relatively small frequency:spectrum` ln such instances the advantages of the system shown inFigure 1, whereby one side lband is partly or wholly suppressed, may beachieved Without significant contamination of the respective signals,bylimiting the band width of one of the input signal waves to adesiredamount for example, by means of a low pass iilter 35. Under theseconditions the Wide band signal component of the output wave of lter'2.3 is not signicantly contaminated by the narrow band signalcomponent. By a suitable selection of the cut-ofi frequencyl of 4thenlter 5S at the receiver Vthe vefiects of the Wide 'band signal on thenarrow band signal may be minimized` In a practical arrangement of asuppressed side band system having a channel width of l mc./sec. and asampling frequency of 3.75 rnc/sec., the iilters 36 and 58 may have acut-oil frequency of .5 inc/sec.

Referring novT to Figure 2, the system there shown comprises foursampling tubes |00, |92, |84 and |06 which may be identical to thesampling tube gli) described in connection with the system shown inFigure l. Each of the tubes itil, iii2, |84 and Ict comprises a rst gridto which an individualsampling signal is applied, and an anode connectedto a source of positive potential B+ through a load resistor |08 whichis common to all of the tubes. The anodes of the tubes are coupled incommon to a low pass lter |09 to produce a resultant output Wave whichin turn is applied to a radio frequency transmitter and modulates thesame in conventional manner.

Each of the tubes further comprises a second grid Which'in the ycase ofthe tube 80 is connected to an input terminal ||ll serving as a sourceof one of the signal Waves to be transmitted, which in the case of tube|02 is connected to an input terminal l 2 serving as a source of asecond signal Wave to be transmitted, which in the case of tube |04 isconnected to an input terminal H4 serving as a source of the thirdsignal voltage to be transmitted, and which in the case of tube |06 isconnected to the input terminal H4 through a phase inverter i6,

The tubes each embody in the rst grid circuit thereof aresistance-capacitance network Whereby the tube is maintainednon-conductive except for predetermined brief intervals when thesampling signal applied thereto has a high positive Peak value, suchnetworks being shown as ||8, |26, |22 and |24 respectively.

The sampling tubes operate to sample the si.,- nal voltages in apredetermined sequence and are actuated by appropriate phase relatedsignals derived from a sampling signal oscillator |26. Moreparticularly, sampling tube |00 is actuated by a n tube d4 .by asampling-signal havinga phase indicated as and sampling tube |06 .by asampling signal having a phasexindicatedas 270.

The Youtput -of each of fthe sampling .tubes .is basically a series 'ofpulses having an amplitude determined by the amplitude of the respectivesigna-l Waves applied to the third grid thereof and having a repetitionfrequency determined by the frequency of the oscillator |26. Thesepulses are shown in lthe wave forms adjacent to the tubes and areindicated as |28, |30, |132 and |34 respectively. As will be noted the;pulses |30 have a phase position displaced by from the Yphase positionof the pulses |23 and, due to the -band limitingr action of'the nlter-i09, thesetWo-sets -of pulses effectively combine to produce a:substantially sinusoidal wave |29 superimposed on a reference level. As

indicated vby the Wave form shown, the value of the reference level isdetermined by the absolute values of the amplitudes of the pulses |28and |30, whereas the amplitude of Vthe sinusoidal Wave is determined bythe difference in the amplitude values of the -said pulses. Thefrequency of the 4Wave -i2v9 `is determined by the frequency of thesampling signal source R|2|5 Vand in the specific system being describedthese two frequencies are the same.

The pulses |32 have a phase position of i90L1 relative to the Yphaseposition of pulses |28 Whereas the pulses |34 are displaced .180 fromthe pulses |32 and, because of -the phase inverter |.|6, have a negativepolarity `relative to pulses |32. Upon Kcombining pulses |32 and |34,and dueto the band limiting action-of filter |09, there will be`produced a sinusoidal Wave |3| with zero reference level and anamplitude proportional to the amplitude of the signal voltage-at inputterminal |44. It will be seen thatthe wave v|-3| has the -sameirrequencyas Wave V|29 and -is displaced 90relative-towave |29. These wavesmaytherefore be combined in the manner discussed in connection with Figurel to produce an output Wave having an amplitude and phase determined `bythe amplitudes of the waves `|29 and |31. The resultant Wave appearingat the -output of'lter |09 has a reference level 'component asdetermined by the absolute magnitudes ofthe signals at input terminals|10 and |I'2 and a sinusoidal component at the sampling frequency havingan amplitude and phase determined by the amplitude of the signal atinput terminal ||4 and the ampltudeidiierence of the signals at inputterminals ifi-0 and l2.

At the receiver location the original intelligence may be recovered by acomplementary sampling system and :for this purpose a Wave having ,the`form of that existing at the output of ilter |69 is derived fromv areceiver |40 and applied to each of sampling tubes 42, |44, |46 and |48.:Sampling tube "|42 may be similar to the Ysampling tubes Vpreviouslydescribed and may comprise a first grid to which a sampling signal isapplied, a third grid to which the Wave from receiver |40 4is suppliedand an anode energized through a load resistor |50. Tubes |44, |46 and|48 may be similar to tube |42, Athe anodes of each thereof beingenergized through load resistors |52, |54 and |56 respectively. As willbe seen from the drawing, tube |42 serves to supply one output terminalindicated as |t0, tube v|44 serves to supply a second output terminalindicated as |62 and tubes V|45 and `|48 are interconnected by a phaseinverter |66 `to supply a third output terminal indicated as |64.Suitable low 9' pass lter elements |68, |l0 and |72 may be provided inthe respective output circuits to limit the frequency spectrum of eachoutput signal.

The sampling vtubes operate to lsample the' Wave from the receiver I()at predetermined time intervals in synchronismY with the samplingprocess at the transmitter, and for this purpose there is provided a.sampling signal oscillator l'lfiA adapted to produce four samplingvoltages displaced 90 relative to each other and having a frequencyequal to the frequency of the oscillator |26. Tube |42 is supplied witha sampling signal indicated as tube me with a sampling signal at 180,tube IGS with a sampling signal indicated as 90, and tube |48 with asampling slgnafl indicated at 270. Each of the tubes is arranged to beconductive onlyduring the positive peak values of the respectivesampling signal, and for this purpose the rst grid circuits thereofembody resistance-capacitance networks |10, |10, |80 and |82respectively, which operate in the same manner as the similar networkspreviously described.

Tube |42 serves to sample the incoming wave from the receiver lili) atinstants thereof corresponding to the positive peaks of the wave |29whereby there is formed at the load resistor a series of pulsescorresponding to the pulses |28 originally derived from the signalapplied to input terminal ||0. Similarly tube |44, which is madeconductive at an interval one-half cycle later than tube |42, samplesthe vreceived wave at instants corresponding to the troughs of the wave|29 so that there is formed at the load resistor |52 a series of pulsescorresponding to the pulses |30. Tubes |46 and |48 sample the receivedwave at instants in phase quadrature to the sampling by tubes |02 and|54 to produce, at the respective load resistors |54 and |50, pulseswhich correspond to the pulses |32 and |34 respectively but which havean enhanced amplitude proportional to the reference level of the wave|20. By means of the phase inverter |66 this reference level componentis effectively cancelled at the output terminal |64.

It is thus seen that by means of the system of Figure 2 three inputsignal voltages may be transmitted over a single channel without thereoccurring significant contamination or cross-talk between the respectivevoltages. More particularly by reason of the sampling and desamplingactions of the tubes |00, |02, |42 and |44 which take place at 180intervals of the sampling cycle, the input waves at terminals H0 and ||2may be combined, transmitted and thereafter separated to obtain outputsignal waves substantially identical to the input signal waves.`Furthermore, by sampling the signal a't terminal I ld in a manner toproduce a carrier wave in quadrature with the wave produced by tubes |00and |02 and having a substantially zero reference value, and by means ofthe phase inversion process at the receiver, the original input wave isreproduced without there occurring therein contaminating componentsotherwise produced by the reference level component of the ,wave |20.

The embodiment of the invention shown in Figure 2 is particularlysuitable for single channel transmission and reception of three signalwaves of the type produced in a dot-sequential three color televisionsystemA As previously pointed out, it appears that the eye is lesssensitive to changes in chromaticity than to changes in brightness.Accordingly, the full requirements of the eye may be satisfied in acolor television system by meansV of a rst image component signalcontaining information concerning thebrightness of the image and havinga relatively wide frequency spectrum and by two additional componentsignals with information concerning image chromaticity and havingrelatively narrow-l frequency spectra. The system shown in FigureA 2 iscapable of transmitting maximum detectable information in conformancewith the above principles.

The heretofore proposed dot-sequential sys-l' tems for transmitting acolor television signals color television system with symmetricalsampling, each signal must be sampled at no greater rate than two-thirdsthe maximum band-pass frequency of the channel if cross-talk is to beavoided. On the other hand, in order to transmit the desired picturedetail it is necessary to use a vsampling frequency which producessignal samples at a rate greater than the above noted critical value.

The system illustrated in Figure 2 lmakes use of non-symmetricalsampling. More particularly, as will be noted, theA signals at terminalsH0 and |!2 lare sampled at 180 intervals once eachY sampling cycle-andthe signal at terminal Il is sampled in quadrature to the rst twosignals and twice each sampling cycle.

In the non-symmetrical sampling as shown in Figure 2, the samplingfrequency for the waves.

at input terminals ||0 and ||2 is equal to the maximum band frequencyofthe transmission channel as determined by thelter |09. Thus, forV agiven maximumffrequency of the transmission channel, a higher samplingfrequency may be used While still permitting the individual samples.toattain a zero value prior tothe occurrence of the succeeding sampleand with zero cross-talk between the waves of input terminals IV and|I2. The wave from the input terminal lili is sampled in quadrature tothe waves at terminals |I0 and ||2 and components of the wave orterminal lill may be introduced into the signal produced by the twowaves from terminals H0 and H2. However, because of the inversion of thepolarity of the third wave by the phase inverter H6 each succeedingsampling period, andv because of the absence of a second inversion inthe receiver systems supplying the output terminals |00 and |62, theVcomponents of the third wave so introduced into the first and secondwaves are effectively .cancelled at the receiver position.

The above described action may be modified to a'certainextent because ofthe suppression of one side band'of the composite wave by the ilter |09.

However, asA pointed out in connection with the embodiment of theinvention illustrated in Figure 1, the cross-talk brought about bysuppressing the side band may be minimized by suitably limiting themaximum frequency of the wave at terminal |11, for example by low passlter |86. Since in a color television system this wave may be used totransmit information to which the eye is relatively insensitive, alimiting Vci its maximum frequency does not produce visual deteriorationoi the color information. In a specic example, in which the transmissionchannel has an allowable band width of 4 megacycles, the vsystem shownin Figure 2 permits the use of a sampling frequency of 4 mc./ sec.without serious cross-talk when the signal at input terminal l i4 islimited `to a maximum frequency of i mc.,/sec., and the lter i12 has acorresponding cut-off value.

vThe system shown in Figure 3 illustrates another embodiment utilizingthe principles of the invention. The system shown comprises six samplingtubes shown as 200, 202, 204, 206, 208 and 210, which may be identicalto the sampling tubes heretofore described and which have their anodesenergized through a common load resistor 212 and connected to a low passfilter 2H which defines the band width of the transmission channel. Thethree signal waves to be sampled are applied to input terminals 214, 216and 218, input terminal 2m being connected to the third grid of each oftubes 200 and 202, input terminal 2I6 being connected to the third gridof tube 204 and through a phase inverter 220 to the third grid of tube266, and input terminal 2I8 being connected to the third grid of tube208 and through a phase inverter 222 to the third grid of tube 2 I0.

.The iirst grids of each of the tubes are actuated `by suitably phasedisplaced sampling signals derivedfrom a sampling oscillator 224, thesequence of the sampling signals being such that tube 200 is actuated atphase position, tube 202 at 180, tube' 204 at 0 simultaneously with tube206,'tube 206` at 180 simultaneously with tube 202, tube 206 at 90L7 andtube 210 at 210. Each of the tubes embodies a resistance-capacitancenetwork whereby the tube is conductive only during the positive peakvalues of the sampling signals, such networks being shown as 224. 226,228, 230, 232 and 234 respectively.

The output of each tube is basicallyT a series of pulses havingamplitudes proportional to the amplitude of the corresponding inputsignal wave and occurring at twice the frequency of the samplingsignals. These pulses have been shown in the wave forms adjacentto eachtube as 236, 238, 240, 242, 244 and 246 respectively. In the case oftubes 200 and 202, the output pulses have the same polarity and becauseof the band limiting action of the lter 2l i, these pulses combine toproduce a reference level wave having an envelopecorresponding to theenvelope of the wave initially applied to terminal 2 I4 such asindicated at 248. Since the input signal to tube 204 is applied inopposite polarity to tube 206, the output pulses of these tubeseffectively combine to produce a sine wave at the frequency of thesampling signal and having a zero reference level and an amplitudeproportional to the amplitude of the signal at terminal 216 as indicatedat 250. Similarly, the input signal to tube 208 is applied in oppositepolarity to tube 2I0 and the output pulses of tubes 208 and 2 l0, byreason of the band limiting action of the filter 2| I, combine toproduce a sine wave 252 at the frequency of the sampling signal, whichwave has a zero reference level, an amplitude proportional to theamplitude of the input signal at terminal 2I8 and bears a quadraturerelationship to the wave 250,.

There will thus appear at the-output of filter 2l l a composite wavehaving a reference level as determined by the Wave 248 and having anamplitude and phase of sine wave component as determined bytheamplitudes of the waves 250:

and 252. This composite wave serves to modulate a transmitter 254 in anyconventional manner.

At the receiving position the composite wave is recovered from areceiver 256 and applied to the sampling tubes 260, 262, 264, 266, 268.and

210, by means of which a complementary sam. The sampling plied to thethird grid of each of the tubes whereas sampling signals derived from agenerator 258 operating at the frequency of the generator 224 andbearing a predetermined phase relationship are supplied to the rst gridof the tubes, tube 260 being energized by a sampling signal at 0 phase,tube 262 by a sampling signal at 180 phase, tube 264 by a signal at 0phase, tube 266 by a signal at 180 phase, tube 268 by a signal at phase,and tube 210 by a signal at 270 phase.

.The output of tube 260 will be basically a series of pulses having anamplitude proportional to the sum of the amplitudes of the pulses 236and 240 whereas the output of tube 262 will be a series of pulses havingan amplitude proportional to the diierence in amplitudes of the pulses238 and 242. In effect, therefore, the wave at the input of a low passfilter 294, which is common to the anodes of tubes 260 and 262, will bea composite wave having a reference level and a superimposed sine wavecomponent. The latter component is suppressed by the filter 294 so thatonly the reference level component remains, which component is thussimilar to the signal originally applied to input terminal 2| 4.

The output pulses of the tube 264 are similar to those of the tube 260and the output pulses of tube 266 are similar to those of tube 262.However, by means of a phase inverter 206 interconnecting the anodes oftubes 266 and 264, the reference level component brought about by thesignal from terminal 2M is cancelled and the subsequent passage of theresultant signal through a low pass filter 298 produces an outputvoltage' similar to the voltage applied to terminal 2l6.

Since the sampling by tubes 260, 262, 264 and 266 takes place atinstants when the Wave 252 is at zero potential, there will be nocomponent of the wave at the terminal 218 in the outputs of filters 294and 298.

The output pulses of the tubes 268 and 210 will be similar to thosederived from tubes 208 and 210 and will contain a reference levelcomponent which is derived from the wave 248. This component iscancelled by a phase inverter 300 interconnecting the anodes of tubes268 and 210, and, by means of a low pass nlter 302, an output wavesimilar to that initially applied to the terminal 218 is produced.

As will be noted, the system shown in Figure 3 is a non-symmetricalsampling system as pointed out in connection'withV the system shown in`lig'ure 2. Accordingly, the. same advantages areV attained as aboveoutlined. Thus inthe specic embodiment illustrated in Figure 3', inwhich the pass band of theV transmission channel is to 4 mc./sec; asdetermined byrnlter 2l I,

the sampling frequency of the oscillators 224 and 2,58 is 4 mc./sec.

Since With the above-given specific values the sampling frequency ofoscillator 221i is .substantially at the cut-off frequency of the lowpass filter 2li, one side band of theresultant wave produced by waves250 and 252 will be suppressed Yalmost entirely and a phase modulationcomponent, as determined by the frequencies of the input signal waves,may be introduced. For a color television system wherein'only one signalwave need be of large band Width and the remaining signal -waves can belimited in their maximum frequency without visual deterioration of theimage, cross-talk due to such phase modulation may be reduced to atolerable value by suitably limiting the frequency range. of the latterwaves. Thus in the system shown in Figure 3 there may be provided forthis purpose a low pass filter 304 to which the signal from inputterminal 2I6 is applied, and `a low pass filter 306 to which the signalfrom input terminal 218 is applied. Y

For the specic operating conditions described in Figure 3, filter 304mayhave a `pass band of 0 to 2 mc./sec. and filter 305 may have a passband of A0 to 1 mc./sec. At the receiver location lters 298 and 302 mayhave the same respective band widths.

In some instances, particularly in view of the z' band pass limitingaction offilter 294 it may be desirable to correspondingly limit thepass band of the signal at input terminal 21.4, and for this purposethere isprovided a low pass filter 308 having similarly a band pass of 0to 3.8

mc./sec.

With the specific frequencyvalues given in connection with theembodiment shown in Figure 3, it will be noted that the rate ofoccurrence of-the pulses 236 and 238 in combination is greater than themaximum transmission frequency of the filter 2l l. Under theseconditions the filter 2H substantially restores the wave Y form of thesignal Wave originally applied to the third grids of sampling tubes 200and 202.

`Under these conditions the sampling tubes 200 and 202 may be eliminatedif desired and the output'of filter 308 may be connected directly to theinput of nlter 2H. Such a modification, whereby the output of filter 308is connected directly to the input of lter 2H, may be indicated in thoseinstances when it is unnecessary to use dot-interlace. principles forimprovement of image resolution. Similar considerations apply at thereceiver position, where the sampling tubes 260 and 262 may beeliminated and the output of the receiver 256 may bedirectly connectedto the input of filter 294.

While I have described my invention by means of specific examples and inspecific embodiments, I do not wish to be limited thereto, for obviousmodifications will `occur to those skilled in the art without departingfrom the spirit and scope of the invention. I

`What I claim is:

lfA signal transmission system comprising individual input channel meansfor three intelligence signals, first and second sampling systems, meansto actuate said sampling systems substantially in phase quadrature at agiven carrier frequency, one of said sampling systems upon'actuationbeing adapted to produce an out- -by the amplitude of a first of saidintelligence signals, means for coupling a second of said input channelsto said other sampling system to thereby produce a second output signal,means to couple the third of said input channels to the said secondoutput signal to produce a first resultant signal having an amplitudereference level and amplitude variations at said carrier frequencydetermined by the amplitudes of said second and third intelligencesignals, and means to supply said first output signal and said resultantsignal to a common transmission'channel to thereby produce an outputwave having reference level and amplitude variations proportional to theamplitude variations of said intelligence signals and having side bandcomponents each having a frequency spectrum determined by the frequencyspectra of said intelligence signals.

2. A signal transmission circuit as claimed in claim 1 comprising meanscoupled to one of said input channels to partially suppress thefrequency spectrum of one of said intelligence signals, and meanscoupled to said common transmission channel to at least partially`suppress the spectrum of one of said side band components.

3. A signal transmission system as claimed in claim l wherein saidsampling system adapted to vproduce an output signal at said carrierWave having an `amplitude reference level independent Yof the amplitudeof an applied input signal, comprises two sampling elements havingindividual -input circuits and common output circuits and means `toapply said first intelligence signal to the input circuit of one of saidsampling elements in a given phase and to the input circuit of theAother of said elements in phase opposition to said given phase, whereinsaid second sampling system comprises a third sampling element having aninput circuit and an output circuit and means to apply said secondintelligence signal to the input circuit of said third sampling element,and wherein said means to couple said third input channel to said secondoutput signal comprises a fourth sampling element having an inputcircuit and-an output circuit, means to apply. said third intelligencesignal to the input circuit of said fourth sampling element, and meansto actuate said fourth sampling element at said carrier frequency inphase opposition to the actuation of said third sampling element..

4. A signal transmission system comprising an input channel for an inputwave comprising two nents, one of said carrier wave components beingindicative of the value of one intelligence signal and the otherA ofsaid carrier wave components and said reference level component beingindicative of the values of two other intelligence signals, av nrsttransmission path coupled to said input channel, a sampling .1 systemadapted to produce 'an output signalhaving amplitudevariations de.termined Ahyarmalitude .variations of a Wave ap- '.plied ythereto .andsubstantially `independent of deference level variations of said.appliedpwave means i for. coupling saidfsampling system v'to I saidrst. transmission .path toithereby apply said .inlput'waveto saidsampling system, means toactu- -ate saidsamplingsystemat:saidcarrierzfrequency -atzgiven .phaseintervalsto:thereby derive from vvsaid inputzwavelaJlrstintelligence signal having,an amplitude 'determined by uthe amplitude of fonepf said carrier,Wavecomponenta a.;second -transmissionpath .coupled to said. inputchannel, -andmeans; to'derivezfrom said second transmis- :'sionlpathsecond and l'third intelligence'signals 4:having amplitudes determinedbythe amplitude :ofthe other of saidcarrier wave components and theamplitude ofv said reference level component, Isaid latter x meanscomprising a. second sampling :system and means tto cnergizesaidsecondsampling system at'said'carrier frequency in vphase quadrature. tothe actuation of saidrst sampling system.

A.5. A signaltransmission circuit Vasaclaimed in claim '4 in .which the.frequency spectrum .of'one Aof '.the side band components of said inputWave nis 4atleast .partially suppressed relative to .the 4frequencyspectrum ofthe other ofthe side band -components 'of' said inputv wave,.and further Acomprising means coupled to the :output of one .of:saidfsampling systems:to partially suppress the spectrum oftheintelligence signalproduced by .the said sampling system.

J6.. #Arssignaltransmission systemes claimed in claim .4 :whereinsaidsampling system adapted 'to produce an output signalhaving amplitudevariations determined by amplitude variations of a wave'applieditheretosubstantially independent "of .reference level variations of saidapplied Wave -scomprises two vsampling elements actuated infphasezopposition at said carrier frequency., said `sampling: elementshaving common input circuits tand. individualoutput circuits, andineansto in- "terconnectithe `said output circuitsin phase op- .'position,andwhereinsaid means to derive from fsai'dseconditrans1mssionpath twointelligence 4signals' vhaving amplitudes determined bythe'amaplitudezof `the j said. other. carrier lWave component :and 4theiamplitudeof the-said reference'level component 'comprises .third andfourth sampling felements having .input :circuits vcoupled to said.,input1.channel.and having individual output circuits, said rthird :andfourth -sampling elements -theing .actuated in -.phase oppositionVrelative to leach .other IandJin phase quadrature relative to :saidfirst fand second Asampling elements.

"7. Asignalftransmission system, comprising a .rst channelfo-r affirstintelligence signalY having a varying vamplitude and having a given fre-..quency-spectrum,a second channel for a second :intelligence signalhaving a .varyingfamplitude and having a secondgivenfrequency.spectrum.first and secondsampling'meanseach having'an .inputcircuit and an outputcircuit, a source of avwave of given frequency,.means to couple said.first .and second channels to .a respective .one of the input circuitsof said sampling means, means to couple the -output circuits 'of 'said`sampling means in common to a thirdchannel, .means to tactuate -saidsampling means substantially in phase quadrature at the frequencycfs-aid Wave to thereby .produce in said third channel-a .carrier .wave`having side band components each :having i a .frequency ,spectrumdetermined by the i'frequency'spectraioirsaidV intelligence 'signals-andmeans coupled tosaidthirdlchannel:totat' least claim '7. further.comprising meansv coupled tosaid -rstchannel .to partially 'suppressthefrequency spectrum of said,..rst intelligence signal.

.9. A-signal transmission vsystem.comprising-an inputcchannel :for aninput wave. comprising vtwo carrier 'Wave components .having .the samefre- ;'quencyand arranged-substantially in phase quadzra.ture,;thefrequency-spectrum'of'one of the side -band icomponents .of said vinputWavebeing at :least partially .suppressed relative .to .the frequencyspectrum `ofthe other of the sideband components of said input'Wa-ve,said .carrier-Wave componentsxbeing teach Aindicative o-f thevalue `ofanintelligence signalyrst'and second'sam- .pling means zhaving input.circuits connected in common togsaid f input ychannel 'and havingindividual output circuits, `means 'to actuate said Sampling .means:substantially in .quadrature .phaserelationshipat theifrequency of saidcarrier Wave.componentsithereby to produce Y'a different intelligencesignal in each of theisa'id'output circuits, andmeafnscoupled .tothe-,output circuit .of one'of said 'samplingmeans .to partially.suppress .thefrequencyspectrum of the intelli- .gencetsignalproducedinthe said output circuit.

10. A .signal transmission Vsystem comprising individual input channelmeans; for three intelligence signals, iirst .andsecond samplingsystems, means to `actuate isai'd sampling .systems sub- :stantially inphaseaquadrature at a. given carrier tfrequency, each :of vsaid sampling:systems upon actua-tion at vsaid. carrieinfrequency being `adapted toproducean output Wave atisaid .carrier frequency having an amplitudereference level in- ;depemdent of the amplitude of .the input'signalapplied to saidsamplingsystem and having amplitudevariations .determinedby the amplitude .of .the .saidapplied input signal, means for couplinga.i'lrs't'of saidinput channels to one of said .sampling systemstothereby produce a rst out- :put AWave atEs-aid .carrier frequency havingam,-

;plitudevariations determined 4by the amplitude ,of a'iirst of saidintelligence signals, means for couplingasecond vof said input channelsto the .'.otherzof said sampling syste-ms tothereby pro'- 'duce asecond'output wave at said carrier frequency in ph-ase'quadrature tosaid nrst output Wave :and having amplitude variations `determined Y.bythe amplitude of a second of said intelligence signals, andmeans'tocouple said rst `andisecond output waves -and the third of saidintelligence signals to a common transmission channel to therebyproducea resultant Wave at .said .carrier frequency .having 'amplitude and.phase variations vdetermined by the amplitude variations'of 'saidflrstand second output waves vand having areference level determined bythe amplitude of -saidfthird -intelligence signal.

'11. .A signal transmissioncircuit-as claimed in claim lwherein said`resultant Wavehas side handA componentseach having av frequencyspectrum determined by the frequency. spectraof said intelligencesignals, and further .comprising means vcoupled to said commontransmission channelito at leastppartially suppress the frequency'spectrumzof oneof said side band compos nentsrelative tot the frequencyspectrum of .the 'other of saidfside .band components.

12. A signal transmission circuit as claimed in claim 11 furthercomprising means coupled to said first input channel to partiallysuppress the frequency spectrum of said rst intelligence signal.

13. A signal transmission system as claimed in claim wherein said firstsampling system comprises two sampling elements having individual inputcircuits and common output circuits and means to apply said firstintelligence signal to the input circuit of one of said elements in agiven phase and to the input circuit of the other of said elements inphase opposition to said given phase, and wherein said second samplingsystem comprises two sampling elements having individual input circuitsand common output circuits and mea-ns to apply said second intelligencesignal to the input circuit of oneL of said latter sampling elements ina given phase and to the other of said latter sampling elements in phaseopposition to said given phase.

14. A signal transmission system as claimed in claim 13 wherein saidmeans to couple the said third intelligence signal to the said commontransmission channel comprises two sampling elements having inputcircuits connected in common to the third of said input channels andoutput circuits connected in common to said common transmission channeland means to actuate said two sampling elements in phase opposition.

15. A signal transmission system comprising an input channel for aninput wave comprising two carrier wave components having the samefrequency and arranged substantialliT in phase quadrature and a thirdcomponent establishing a reference level for said carrier wavecomponents, said components being indicative each of a diierent one ofthree intelligence signals, rst, second and third transmission pathscoupled to said input channel, means coupled to said first path forderiving from said input wave said third component to thereby produce afirst output signal having amplitude variations determined by amplitudevariations of said reference level component of said input wave, firstand second sampling systems, means to actuate said sampling systemsubstantially in phase quadrature at the frequency of said carrier wavecomponents, said sampling systems being adapted to produce outputsignals having amplitude variations determined by amplitude variationsof a wave applied thereto substantially independent of reference levelvariations of said applied Wave, means to couple said secondtransmission path to one of said sampling systems to thereby produce asecond output signal having variations determined by the amplitudevariations of one of said carrier wave components, and means to couplesaid third transmission path to the Aother' of said sampling systems tothereby produce a third output signal having variations determined bythe amplitude variations of the other of said carrier wave components.

16. A signal transmission system as claimed in claim 15 in which thespectrum of one of the side band components of said input wave is atleast partially suppressed and further comprising means coupled totheoutput of one of said sampling systems to partially suppress thespectrum of the output signal produced by the said sampling system.

17. A signal transmission system as claimed in claim 15 in which each ofsaid sampling systems comprises two sampling elements having commoninput circuits and individual output circuits, means to actuate said twosampling elements in phase opposition and means to interconnect the saidoutput circuits of said two sampling elements in phase opposition.

18. A signal transmission system as claimed in claim 17 wherein saidmeans coupled to said first path for producing said first output signalcomprises two sampling elements having input circuits connected incommon to the said rst path/and output circuits connected in common toan output channel, and means to actuate said sampling elements in phaseopposition.

ROBERT C. MOORE.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 1,928,093 Coyle Sept. 26, 1933 2,021,743 Nicolson Nov. 19,1935 2,471,253 Toulon May 24, 1949

